In June, NASA officials announced some distressing news: America’s next great space telescope won’t launch next spring, as they had hoped. Engineers needed more time to finish it. Their new deadline, they said, is 2021.

To explain the delay, officials brought in Tom Young, a highly respected engineer who has been involved with NASA since the 1970s. Young ran through a litany of problems, each more groan-worthy than the next. Engineers had used the wrong solvent to clean the space observatory’s propulsion valves. They had applied too much voltage to the spacecraft’s pressure transducers. When they shook the spacecraft to test whether it could withstand a rocket launch, dozens of bolts broke free and scattered into its hardware, leading to a weeks-long effort to find them.

But there was also a deeper problem. Unlike technical errors like damaged valves or scorched transducers, this problem was intangible, invisible. The tremendous schedule delays and cost overruns of the James Webb Space Telescope, Young said, were also a result of “excessive optimism” from the mission’s engineers, scientists, and program managers.

NASA had aimed high to build the world’s most powerful space telescope, capable of seeing the faint light from the most distant stars and galaxies, of detecting hints of life-giving molecules in the atmospheres of faraway planets. The nearly finished result is a tremendous feat of human ingenuity—but it exceeds an initial price tag by billions of dollars, and the initial launch date by 14 years.

Optimism is essential to NASA’s success. It is difficult to imagine a group of pessimistic—or even realistic—people enthusiastically setting out to do something that has never been done before, like putting a human being on the moon or a driving a robot on Mars, and then actually doing it.

“You have to be optimistic to beat gravity and to do the amazing things that NASA does,” says Lori Garver, who served as the agency’s deputy administrator from 2009 to 2013. “On the other hand, that has caused us to overpromise and make mistakes.”

Financial overruns and schedule delays are not unusual for NASA projects. Since the agency opened in 1958, several of its most high-profile missions—the Hubble Space Telescope, the Mars Curiosity rover—have launched into space well beyond their budget and timeline goals. This is, in part, because of the inherent nature of space exploration: When you’re trying to do something no one else has done before, you don’t always know how much work it will take.

“It’s almost never the case that things come in ahead of schedule, and it’s not because of failure to plan,” says Mason Peck, an engineer at Cornell University who served as the NASA chief technologist from 2011 to 2013. “It’s just when you plan for that schedule, disruptions force you into the future. It’s just the nature of the beast.”

Outside government groups have spent years chastising NASA over this, arguing that the space agency could do better. In 2012, the NASA office of the inspector general published a report titled “NASA’s Challenges to Meeting Cost, Schedule, and Performance Goals.” The document was based on interviews with dozens of agency employees, including current and former administrators, the directors of various NASA facilities, and project managers. There were several major challenges, the report concluded, including an underestimation of technical complexity, funding instability, and shifting priorities from presidential administrations and Congress. And the top challenge, the report said, was NASA’s positive outlook.

“It was clear from our interviews that a culture of optimism and a can-do spirit permeate all levels of NASA, from senior management to front-line engineers,” the report said. “Although this optimistic organizational culture is essential for realizing groundbreaking scientific achievement, it can also lead to unrealistic projections about what can be achieved within approved budgets and timeframes.”

Particularly, project managers are “overly optimistic” about how much effort developing and testing new technology will take, the report said.

That’s still the case today, says Paul Martin, NASA’s inspector general, who oversees independent reviews of the agency’s programs, from Earth-observing satellites to Mars rovers. He traces the rise of this mind-set—mission success above all—to the 1960s, when the United States put a man on the moon just eight years after President John F. Kennedy called on the nation to do so. “The optimistic and focused national goals of the Apollo program, coupled with the program’s generous funding profile, set the foundation for an organizational culture that believes nothing is impossible despite significant technical hurdles and other challenges,” Martin says.

The NASA of the Apollo era did not define mission success as meeting cost and schedule goals. These were secondary concerns. Perhaps this kind of mind-set would have been sustainable if the space agency’s budget grew with each passing year to accommodate its ambitions, but it didn’t. It was only a matter of time before NASA’s goals—ever more ambitious, more technically challenging—began to chafe against the prickly realities of time and money.

And yet, the optimistic mind-set that sent Americans to the moon hasn’t budged. “When asked to define ‘project success,’ nearly all the project managers we interviewed responded that a project was successful if it achieved its technical performance goals,” the 2012 report said. “No manager mentioned controlling cost and schedule growth as significant measures of success. Moreover, all described their projects as successful even though many had experienced adverse cost and schedule outcomes.”

Martin says NASA employees call this cognitive dissonance the “Hubble psychology.” The Hubble Space Telescope was not an immediate success when it reached space in 1990. The telescope took much longer to develop than promised, exceeded its budget, and launched with a defect in its primary mirror that took several missions to repair and maintain. But today, Hubble is considered a national treasure, and its chaotic beginnings have largely been forgotten.

“As long as you bring back—in Hubble’s case—pretty pictures, all your cost overages and schedule delays will be forgiven,” Martin says. “Because what’s important is the science at the end, not how you got there, how messy or over budget or over schedule you’ve been. That may be somewhat of an overstatement, but that’s sort of the mentality: that all sins will be forgiven if you bring back the pretty pictures.”

This is the outcome the Webb team seems to be banking on. Webb is worth the wait, program officials have said, over and over again, as the costs have mounted and the finish line has moved further away. They hope the payoff will overshadow the pains of the process.

Most people are optimists, research suggests. In a work setting, optimism can be an energizing force. “People enjoy being optimistic more than pessimistic,” says Julie Norem, a psychology professor at Wellesley College and the author of The Positive Power of Negative Thinking, which argues that for some people, optimism is an ineffective strategy. “They enjoy the confidence of thinking that everything is going to work, and so that can be motivating. It can lead people to potentially try something they might not try otherwise, because they’re so positive and sure that it’s going to work.”

In groups, particularly those working toward a common goal, optimistic thinking can be infectious. “If you take a bunch of people working on a project and everyone has a little bit of bias—and the bias that people have is quite mild, just a little bit of an overestimation of the positive and underestimation of the negative—you put them together, and the bias just becomes bigger,” says Tali Sharot, a neuroscientist at University College London who studies the human brain’s inclination toward optimism.

In this scenario, it can be difficult for people to vocalize concerns, particularly negative ones, Norem says. “When that’s the top-down message, then it’s very hard to bring problems that you anticipate to light because nobody wants to hear them,” she said. “It ends up, in that kind of culture, taking a lot of courage to bring up the negative possibilities. Once there’s a commitment to a plan, nobody wants to hear anything against the plan.”

Garver said she saw this in action during her time as NASA’s associate administrator. “Honestly, it’s just everywhere,” she said. We “tried to encourage people to speak up but it continues to be shocking sometimes when that didn’t happen. Of course, there’s 18,000 people, 40,000 contractors. Our message for openness wasn’t enough.”

Martin’s report found the same effect. “Many interviewees indicated that project managers and senior NASA leaders are often hesitant to admit they cannot overcome technological challenges or meet mission requirements within the funding profile provided,” it said.

NASA has canceled some programs because of cost and time overruns, Martin says, but these have been smaller projects costing several hundred million dollars, a pittance compared to Webb’s lifetime cost of $9.6 billion. It’s the biggest astronomy missions—the most complex, technically challenging efforts—that are at the greatest risk of missing targets and deadlines, and the most difficult to say no to, especially when so much has already been invested. “Once you’ve spent $9 billion, the thinking would be: What’s another billion?” Garver says.

Nearly 30 years after Hubble launched and taught NASA a valuable lesson, agency leaders appear to be making the same mistakes. The Government Accountability Office (GAO) reported last month that NASA’s major projects have experienced average launch delays of 12 months in 2018, the worst in a decade. Perhaps the blame rests with the way humans interpret the past, says Chris Dawson, a professor at the University of Bath who studies labor economics. “Generally we blame past failures on external influences and take credits for projects that went well; this means people can discount past evidence of how long a task should take,” he says. “We forget past failures and focus on past successes.” And NASA has many successes to choose from.

Still, NASA knows budgets and schedules are finite, even as the scientific possibilities are not. About a decade ago, the agency vowed to temper its can-do attitude in response to an earlier GAO report. “The agency issued a corrective action plan that established a definition of success for its portfolio of projects,” according to the inspector general’s office. “Specifically, the agency established that success would be defined as completing its portfolio of major development projects within 110 percent of the cost and schedule baseline.” NASA said it hoped to meet this criteria by 2013.

“They need to be credible and transparent to Congress and the taxpayer about what particular proposed missions will cost, because it’s all about choices,” Martin said. “With a finite budget, if we do this project, then we may not be able to do that project. You can’t do everything.”

Indeed, NASA can’t do everything. But its outlook, since its very inception, has been that it can do anything. Over the years, the mind-set has morphed into a mandate. NASA has become a dream factory, where imagination manifests in technology that has revealed all kinds of wonders, from distant planets to galaxy clusters, and may, someday, detect life on other worlds.

“Finding life outside our solar system and answering such a bold question—it’s hard to put a price tag on it,” Garver said. “However, I believe the taxpayer should expect us to.”

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